"""
自定义的分页组件，以后如果想要使用这个分页组件，需要做如下几步：

在视图函数中
    def pretty_list(request):
        # 1.根据自己的情况去筛选自己的数据
        queryset = models.prettynum.objects.filter(**data_dict).order_by("id")

        # 2.实例化分页对象
        page_object = Pagination(request, queryset)

        # 3
        context = {
            "pretty_list": page_object.page_queryset,   # 分完页的数据
            "page_string": page_object.html()           # 生成页码
        }

        return render(request, 'pretty_list.html', context)

在html页码中：
    {% for obj in pretty_list %}
        {{ obj.xx }}
    {% endfor %}

    <ul class="pagination">
        {{ page_string }}
    </ul>

"""

from django.utils.safestring import mark_safe


class Pagination(object):

    def __init__(self, request, queryset, page_size=10, page_param="page", plus=3):
        '''
        :param request:请求的对象
        :param queryset:符合条件的数据（根据这个数据给他进行分页处理）
        :param page_size:每页显示多少条数据
        :param page_param:在URL中传递的获取分页的参数，例如 /pretty/list/?page=15
        :param plus:显示当前页的 前或者后几页（页码）
        '''
        import copy
        query_dict = copy.deepcopy(request.GET)
        query_dict._mutable = True
        self.query_dict = query_dict
        self.page_param = page_param

        page = request.GET.get(page_param, "1")
        if page.isdecimal():
            page = int(page)
        else:
            page = 1
        self.page = page
        self.page_size = page_size
        self.start = (page - 1) * page_size
        self.end = page * page_size

        self.page_queryset = queryset[self.start:self.end]

        # 数据总条数
        total_count = queryset.count()
        # 计算出总页码
        total_page_count, div = divmod(total_count, page_size)
        if div:
            total_page_count += 1
        self.total_page_count = total_page_count
        self.plus = plus

    def html(self):
        if self.total_page_count <= 2 * self.plus + 1:
            # 数据库中的数据比较少，都没达到11页
            start_page = 1
            end_page = self.total_page_count
        else:
            # 数据库中的数据比较多>7页
            # 当前页 <3时
            if self.page <= self.plus:
                start_page = 1
                end_page = 2 * self.plus
            else:
                # 当前页 > 3
                # 当前页 +3 > 总页面
                if (self.page + self.plus) > self.total_page_count:
                    start_page = self.total_page_count - 2 * self.plus
                    end_page = self.total_page_count
                else:
                    start_page = self.page - self.plus
                    end_page = self.page + self.plus

        # 页码
        page_str_list = []

        self.query_dict.setlist(self.page_param,[1])
        # print(self.query_dict.urlencode())

        # 首页
        page_str_list.append('<li><a href="?{}">首页</a></li>'.format(self.query_dict.urlencode()))

        # 上一页
        if self.page > 1:
            self.query_dict.setlist(self.page_param,[self.page-1])
            prev = '<li><a href="?{}">上一页</a></li>'.format(self.query_dict.urlencode())
        else:
            self.query_dict.setlist(self.page_param,[1])
            prev = '<li><a href="?{}">上一页</a></li>'.format(self.query_dict.urlencode())
        page_str_list.append(prev)

        # 页面
        for i in range(start_page, end_page + 1):
            self.query_dict.setlist(self.page_param,[i])
            if i == self.page:
                ele = '<li class="active"><a href="?{}">{}</a></li>'.format(self.query_dict.urlencode(), i)
            else:
                ele = '<li><a href="?{}">{}</a></li>'.format(self.query_dict.urlencode(), i)
            page_str_list.append(ele)

        # 下一页
        if self.page < self.total_page_count:
            self.query_dict.setlist(self.page_param,[self.page + 1])
            next = '<li><a href="?{}">下一页</a></li>'.format(self.query_dict.urlencode())
        else:
            self.query_dict.setlist(self.page_param,[self.total_page_count])
            next = '<li><a href="?{}">下一页</a></li>'.format(self.query_dict.urlencode())
        page_str_list.append(next)

        # 尾页
        self.query_dict.setlist(self.page_param,[self.total_page_count])
        page_str_list.append('<li><a href="?{}">尾页</a></li>'.format(self.query_dict.urlencode()))

        # 跳转
        search_page = """
            <li class="col-lg-2">
                 <form class="input-group" method="get">
                     <input class="form-control" placeholder="页码" name="page" type="number" min="1" max="{}">
                     <span class="input-group-btn"><button class="btn btn-default" type="submit">跳转</button></span>
                 </form>
            </li>
        """.format(self.total_page_count)
        page_str_list.append(search_page)

        # 加载到html
        page_string = mark_safe("".join(page_str_list))
        return page_string
